Electrovestibulogram: first results in the guinea pig.

This paper describes a method of investigation of the peripheral vestibular system. Electrical stimulations (ES) are applied on the round window of chronically implanted guinea pigs, with and without vestibular stimulation (either per or post rotational accelerations). The whole nerve action potential recorded at the output of the internal auditory meatus, the difference between the two conditions, reveals the change in electrical excitability and thus presumably in discharge rate of vestibular fibres determined by rotational stimuli. This electrical vestibular action potential (EVAP) presents as a mainly monophasic potential with a peak latency to ES of about 0.3 ms. Right and left accelerations versus rest are shown to give responses with opposite polarity, reflecting the inhibitory and excitatory influences of these opposite accelerations, whereas the transfer function of EVAP versus acceleration amplitude appears roughly linear. These observations appear altogether coherent with published mechano-physiological data about individual discharge rates of canal fibres. Also relative amplitudes of acoustical and vestibular responses are in agreement with related number of fibres in the two systems. This EVAP could be the basis of a quantitative evaluation method for the vestibular system, the electrovestibulogram (EVG).